This invention relates to a process for preparing certain titanium and zirconium complexes comprising one or more cyclic, delocalized ligand groups wherein the metal of said complexes is in the +2 formal oxidation state. In a preferred embodiment, this invention relates to such processes wherein the metal is bonded to the cyclic group or groups via the delocalized .pi.-electrons thereof and also covalently bonded thereto via a divalent ligand group. Such complexes are referred to in the art as "constrained geometry" complexes.
In U.S. Pat. No. 5,512,693, the preparation of the foregoing metal complexes by reaction of the corresponding complex in the +3 or +4 formal oxidation state with an n-alkyl Grignard reagent was disclosed. The technique therein disclosed gives improved yields of the desired product, however, due to limited solubility of the Grignard reagents, generally requires the use of an ether based solvent. Disadvantageously, such solvents need to be scrupulously removed from the resulting product in order not to adversely affect the activity of the resulting metal complex as a catalyst component. This introduces a need for a purification step in the preparation. To further commercial preparation of such complexes, it would be desirable to eliminate the need for such a subsequent purification step.
In U.S. Pat. No. 5,491,246, the above metal complexes were prepared by reaction of the corresponding alkoxide complex in the +3 or +4 formal oxidation state with the diene in the presence of a reducing agent. Suitable reducing agents included metals and compounds, specifically sodium naphthalenide, potassium graphite, lithium alkyls, trihydrocarbyl aluminum compounds and Grignard reagents.
The preparation and characterization of certain biscyclopentadienyl zirconium and hafnium diene complexes are described in the following references: Yasuda, et al., Organometallics, 1, 388 (1982) (Yasuda I); Yasuda, et al., Acc. Chem. Res., 18, 120 (1985), (Yasuda II); Erker, et al., Adv. Organomet. Chem., 24, 1 (1985); and U.S. Pat. No. 5,198,401. The preparation of certain Ti, Zr, and Hf monocyclopentadienyl diene complexes lacking the present bridged ligand structure, was described in Yamamoto et al., Organometallics, 8, 105 (1989) (Yamamoto) and Blenkers, J, et al., Organometallics, 6, 459 (1987).